Hey there, @css321.

Welcome to the Community! I'd be glad to offer my assistance.

When you back up your company file, it's always best to do this local on the desktop. Once you have saved your back up to the desktop you could choose to move it to the dropbox, if you prefer to have it there. I recommend using our Intuit Data Protect to save the back up on the cloud. 

You can follow these steps in the article posted below for more details on creating a local back up.

https://quickbooks.intuit.com/learn-support/en-us/back-up-data/back-up-your-quickbooks-desktop-compa...

If you have any more questions, please know I am only a post away. Have a great rest of your day!